Comments on: Desktop Project Part 23: What are the odds of a satellite re-entering over water?http://blogs.discovermagazine.com/badastronomy/2012/04/17/desktop-project-part-23-what-are-the-odds-of-a-satellite-re-entering-over-water/
Wed, 21 Nov 2012 15:12:45 +0000hourly1http://wordpress.org/?v=4.0.5By: icemithhttp://blogs.discovermagazine.com/badastronomy/2012/04/17/desktop-project-part-23-what-are-the-odds-of-a-satellite-re-entering-over-water/#comment-328725
Mon, 23 Apr 2012 05:18:10 +0000http://blogs.discovermagazine.com/badastronomy/?p=43242#comment-328725Oh, and I forgot to mention that the second graph in BA’s original topic has a symmetrical outcome. I wondered why, as the land distribution was anything but symmetrical.

I finally realised that the result is from the many passes over the Earth’s surface to complete the “scan”. It occurred to me that eventually the same land would be traversed twice, once on a north/south direction and then on a south/ north direction. This would devolve to a symmetric pattern of coverage.

I seem to recall that if all the ice was removed from the Antarctic continent, (melted, realistically), then the continental bedrock would “rise again”, alluded to in the quote by jt @23, in the second Wiki link, “… Map is not corrected for sea level rise or isostatic rebound …”, the word “isostatic” being the key word.

The land would rise up, but whether it rises above the new general mean Sea Level, is another matter. I think it would, as the extra water from the melted ice would spread across the whole Earth’s oceans. We are only looking at hundreds of meters of increase in sea level worldwide, (which definitely swamps my house – by hundreds of meters!).

Phil, this has been a very enlightening topic, as it involves Cause and Effect problems that the world faces, and has faced before. I live in Sydney, Australia, where eons ago the eastern shore line has alternated between the sandstone laid down in seabeds, but now form the Blue Mountains west of the city, (OK, that could have also been uplifted tectonically), and out to sea to the edge of the continental shelf, not very far, as it drops away steeply to great depths in the Pacific. Check out any Google Earth map on the global scale where the seabed is depicted.

True, there would be less “dry” land if all the ice melted, but there would still be a significant amount for the remaining population to continue on its merry way. Of course, if the Antarctic melted, then the other great repositories of mass ice (Greenland, Iceland etc.), would also melt, contributing considerably to the sea rise, but excepting already floating sea ice, and icebergs, as they have already displaced their maximum amount of seawater.

#25 ToSeek gives a good explanation, but in case that doesn’t do it for you, here’s another way of looking at it. Let’s imagine two hypothetical planets:

Planet #1 “Ring”: A thin strip of land around the equator, accounting for 5% of the planet’s surface, and no other land. If a satellite around this planet is in a 0 degree inclination orbit, it will be over the equator at all times, and hence over land at all times. So, despite the fact that the planet is only 5% land, a satellite can be over land 100% of the time.

Planet #2 “Cap”: All land in the planet is in a single cap over the south pole, from 45 degrees south to 90 degrees south. After a bit of math, this comes to representing 14.6% of the planet’s surface being covered by land. Now, imagine a satellite in a polar orbit. It will be over land when it’s between -45 and -90 degrees, and over water the rest of the time. Since it travels through an equal number of degrees in an equal amount of time, and there are 180 degrees of latitude total (mirrored to give 360), this implies that the satellite spends 25% of its time over land. This is similar to the case with Antarctica – for a polar orbit, a satellite spends a disproportionate amount of time over the small amount of area near the poles.

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Fri, 20 Apr 2012 19:56:41 +0000http://blogs.discovermagazine.com/badastronomy/?p=43242#comment-328721Phil, I really appreciate this article, it is a perfect accompaniment to discussions I have with some of my more panic-inclined and logical-thinking-deficient co-workers and friends.

A corollary to this that I frequently find myself addressing is the question of “Why, if asteroids and meteors are such a danger to the planet, does space debris not leave large impact craters?” in regards to some of the cases where debris does impact land.

I have explained the relative speed components and mass components repeatedly, but I suspect that a well put together article with similar graphs would be much more helpful than my white board doodles.

“according to wikipedia, the most extreme atmospheric pressures recorded on earth are 108.6kPa in mongolia and 87kPa in during typhoon tip in the north pacific ocean. since these extreme variations in air pressure during extreme weather phenomenon only amount to about a 20% difference, it’s probably safe to say there is no major difference in air pressure at various latitudes.”

ceramicfundamentalist, I think lepton’s talking about the _higher_ atmosphere in the tropics, not the pressure at the surface. Due to various effects like insolation, Hadley circulation, different composition, etc., the tropical stratosphere is higher than the polar stratosphere, and the mesosphere, and so forth, so reentry would be a bit different too.

]]>By: ToSeekhttp://blogs.discovermagazine.com/badastronomy/2012/04/17/desktop-project-part-23-what-are-the-odds-of-a-satellite-re-entering-over-water/#comment-328719
Thu, 19 Apr 2012 02:44:02 +0000http://blogs.discovermagazine.com/badastronomy/?p=43242#comment-328719@11 Chinahand: I think the polar regions get overrepresented when you do the calculations. Think about it: a polar satellite in a low orbit will go over each pole every 90 minutes, or 16 times a day, while it will only hit 32 spots on the equator. So land at the poles counts for more than land at the equator, and there’s land at the poles about 50% of the time.

]]>By: ceramicfundamentalisthttp://blogs.discovermagazine.com/badastronomy/2012/04/17/desktop-project-part-23-what-are-the-odds-of-a-satellite-re-entering-over-water/#comment-328718
Wed, 18 Apr 2012 18:02:13 +0000http://blogs.discovermagazine.com/badastronomy/?p=43242#comment-328718“We probably also need to consider the atmosphere density variation at different latitude, that might be another important variable.”

@ 8 lepton:
according to wikipedia, the most extreme atmospheric pressures recorded on earth are 108.6kPa in mongolia and 87kPa in during typhoon tip in the north pacific ocean. since these extreme variations in air pressure during extreme weather phenomenon only amount to about a 20% difference, it’s probably safe to say there is no major difference in air pressure at various latitudes.

but i don’t bring this up to critique your idea. actually, it gave me the most amazing mental image of a spacecraft plunging to earth through the eye of a hurricane. anyone want to guess on the odds of that mega-disaster?

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Wed, 18 Apr 2012 17:19:54 +0000http://blogs.discovermagazine.com/badastronomy/?p=43242#comment-328717@21… Only parts of Antarctica are above sea level. Approximately half is below sea level, covered in ice down to the bedrock. See the maps here: http://www.zegarkus.com/2007/11/antarctica-with-no-ice.html

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Wed, 18 Apr 2012 17:00:18 +0000http://blogs.discovermagazine.com/badastronomy/?p=43242#comment-328716@17… Jon, Antarctic glaciers slide into the ocean from the land mass, so while there’s deep ice over much/most of the continent, it’s sitting on dry land except for the small portion extending into the sea surrounding it.
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